<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>javascript</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box
    }
    body {
      font-size: 14px;
      padding: 20px;
    }
    ul li {
      line-height: 30px;
    }
  </style>
</head>
<body>
  <ul>
    <li></li>
  </ul>
</body>
<script>
  var regex = /[0-9]+/g
  var str = 'cb12cde456fgh789';
  console.log(str.replace(/(^|[a-z$])/g, 'mm'));
  console.log(str.match(/^(\d{2,})/g));
  console.log(str.replace(/\d{2,3}/g, 'pp'));
</script>
</html>